I milled a circuit board with my Vamp milling machine. The circuit I found on the Internet. It is not your standard LM386 amplifier. It is a clone of a Radio Shack amplified speaker. The Radio Shack circuit has a one transistor pre amp before the LM386. It also has two 100pf caps to keep out RF. The voltage for the pre amp transistor is correctly isolated from the LM386 by using a resistor and a large 220uf cap. I also added a resistor and cap on the output of the amp that Radio Shack seemed to have left off? I also added a anti-Hiss cap and resistor. I milled a PC board and mounted the parts. The board worked but the board lacked soul. So I went old school with this project. Perf Board, Buss Wire, Pins and Point to Point wiring. To top it off I hit my local cigar store for a nice wooden box.
In the picture you can see how I tested the board before going further. I used a MP3 player as a signal source. It was during this process I selected the speaker I was going to use. I built the project with parts I already had!
Using a hole layout pattern I found on the Internet I marked each hole location using an awl. I then drilled each location with a tiny drill bit.
I then drilled the holes with two more bits. Each bit was bigger than the last. This helped prevent some of the tear our you get when you drill wood.
Next I glued in two pieces of wood to hold the PVC plastic mount for the board and battery holder.
The speaker has a indentation on the back of the magnet. I tapped the center of the PVC base. I used a bolt to hit the indentation in the magnet. I put a piece of rubber in between the bolt and the speaker. Now the speaker is held in place with no bolts showing on the outer case.
The unit is wired using shielded cable from the 1/4" imput jack over two the volume control and then onto the board. The volume control has a built in power switch.
The final test was running the amp from a Regenerative Radio. This worked great! No unexpected oscillation as with other amps I tried.
If you want the circuit I used "Google Radio Shack Amplified Speaker Circuit". I just tried it and it showed up in the Google Picture Section.
Email: John a quick question
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